Field of the Invention
The present invention generally relates to a drilling machine, a milling machine, a lathe or any other machine tool, and more particularly to a positioning device for putting an edged tool exactly at a desired position on a workpiece to be machined.
Description of the Prior Art
In an attempt to eliminate the necessity of complicated markings to find in a workpiece a desired position at which the workpiece is to be machined, the inventor proposed a device for putting the center of an edged tool of a machine tool exactly on a selected side of a workpiece, from which side the edged tool can move a measured distance to the desired position (See Japanese Utility Model Publication No. 50-43434).
Referring to FIG. 1, such a proposed device comprises an elongated hollow cylindrical section 21 and a shortened hollow cylindrical section 22, both aligned on a common axis and resiliently connected to each other. In use the two-sectioned cylindrical device is fitted in the chuck 7 of a machine tool in place of an edged tool. The two-sectioned cylindrical device is so adjusted on its level that its shortened end section 22 is below the upper surface level of the workpiece 12 and that its elongated secton 21 remains above the upper surface level of the workpiece. Then, the cylindrical device while rotating is moved towards a selected side of the workpiece 12. When the cylindrical device is brought in contact with the selected side of the workpiece 12, the shortened end section is somewhat displaced with respect to the elongated section as a counter action to the contact with the workpiece, and then the rotation of the cylindrical device automatically stops, indicating that the cylindrical device is put in contact with the selected side of the workpiece 12. Then, the cylindrical device is replaced by an edged tool, and the edged tool is moved a measured distance plus the radius of the edged tool to reach a desired coordinate position in an X-or Y direction.
The proposed device, however, has a few disadvantages: after having found a start position, it is necessary to replace the device by an edged tool for performing required machining. The proposed device is useful only in two - dimensional positioning, or in finding a desired X-and Y-coodinate position, but it is useless in detecting a desired depth in a Z-direction (i.e along the axis of rotation of the edged tool).
Because the two-sectional cylindrical device cannot put its shortened end section offset with respect to its elongated section as a counter action to the contact with the upper surface of the workpiece, the device cannot find a start point from which a desired depth is to be measured in the Z-direction.
With the drawbacks of the prior art in mind the object of the present invention is to provide an edged tool positioning device eliminating the necessity of replacing the positioning device by the edged tool, still permiting a three-dimensional positioning in X-,Y-and Z directions with ease.